best mileage - tailgate up or down?

[Pat]

Jonathan, I absobloominlutely do believe that removing or lowering the tailgate changes the aerodynamics and mileage of pickups. It increases the drag coeficient which makes for poorer mileage.

The aerodynamics of a pickup are such that it essentially carries a "bubble" of air with it in the bed which is almost the same as covering the bed with a tonneau cover. This is design, not an accident. Lowering or removing the tailgate or replacing it with a cargo net, disturbs/perturbs the aerodynamic design and increases drag.

Sorry if it seems counter-intuitive. I used to feel unsettled regarding the little vertical airfoils on the top of airliner wings near the wing roots. How could these things increase performance by exhibiting drag? I finally "got it." Maybe you will too.

Pat

[chrisjbell]

<font color="blue"> I absobloominlutely do believe that removing or lowering the tailgate changes the aerodynamics and mileage of pickups. It increases the drag coeficient which makes for poorer mileage. </font color>

I've heard the same thing, and have seen a few articles that support the reasoning. I used to be a "tailgate down" guy, but have seen enough evidence regarding the aerodynamics that I had to turn my opinion around [img]/forums/images/icons/blush.gif[/img]...

[Pat]

Chris, The tailgate thing is counter intuitive. It wouldn't have been my first guess. I guess that is why it is so easy for the aftermarket retailers to sell various cargo net tailgate replacements and louvered tailgates. More snake oil for the unwary.

P.T. Barnum was right when he said, "there is a sucker born every minute". (and two to take him!)

Pat

[chrisjbell]

Dead on, Pat. I'm keeping the unlouvered gate on my truck in the "up" position from now on. Trying to avoid excess snake oil, eh?

...Chris [img]/forums/images/icons/laugh.gif[/img]

[lonesome]

Pat, I agree with you about drag coefficient with the tailgate up/down. Now my question. I have a louvered tailgate with the "V" notch for fifth wheel/goose neck trailers, so would I get any better fuel milage if when I unhook and have no trips planned to put the stock tailgate back in? Just curious.

Steve

[ric]

Don't know about todays truck, but I'd bet some or all of the following still applies.

In the mid 70's there was an engineering study that suggested, driving around with your tailgate down was supposed to give you a 3% gain in MPG. This was the first part of an engineering school project that evaluated the impact of applying practical areodynamics. The second part, an actual test of the theory proposed in the first part, proved the theory wrong.

As I recall, the first part went on to be cited repeatedly as fact conveniently dropping certain parts of the title and report. Didn't take long for this to take on a life of its own. You may recall after the oil embargo in the mid 70's there was a magazine postcard insert that stated returning the card with $1 would get you the secret to improving the MPG in your truck by 3%. What you got back was another postcard saying that if you drove around with your tailgate down it would improve your gas mileage 3%.

This same study did lead to proving the idea that if you could strap on enough horsepower to an upside down dinning room table floating in the water you could get it to plane like any other boat once you cracked the throttle open.

This started as a joke one night in somebody's campus apartment when the discussion turned to what it would take to get... The first topic was what would it take to get a brick to fly like an airplane... that was scrapped when the group determined the Navy had already figured this out when they strapped enough jet engine into the fuselage of an F4 and it flew.

Other than that I don't know anything about it, except my trucks get terrible MPG and thats what I expected and they are fun to drive.

Later.

[Pat]

Ric, This topic will live on as long as thre are suckers who think buying some aftermarket gizmo will improve aerodynamics better than the maugacturers wind tunnel tests. Tests have been made and not just half baked kids. The bubble of air like having a toneau cover IS the fact.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[ric]

Agreed.

If I was concerned about the cost of ownership, which is what asking about the best MPG is about to some extent, I'd buy a diesel truck and make my own biodiesel fuel to burn in the truck. Search the 'net for biodiesel and see for yourself. Does require some up front investment but it works well even if your truck smells like a deep fryer or peanuts cruzin around da 'hood.

Then there's water... when you crack water into oxygen and hydrogen you can use both to run your gasoline engine with a few mods. The hydrogen part is a little tricky, no smoking.

Later

[Pat]

RIC, Biodiesel has been covered rather well in my "HomePower" magazine as well as some other reading. I used to drive a propane only (not duel fuel) Ford 1/2 ton. It smelled like a gas oven but without the cookies or roast.

There is biodiesel and biodiesel blend available in parts of the country at commercial fueling stations. A friend recently told me of new stations opening that have CNG, propane, biodiesel, and regular fuels. They will be offering hydrogen when/if it is distributed as motorfuel.

Yes, as any general science student knows, an electric current passed through water dissociates it into its constituent elements, hydrogen and oxygen which rapidly reconstitute themselves into oxygen and hydrogen molecules. In theory, you should get all the energy back that you used to split the water when the oxygen and oxygen are recombined to make water again. Sounds great. Like total recycle, man. Unfortunately in the real world there are losses and you actually use more energy "making" hydrogen and oxygen than you get reacting (burning) them to produce heat or process via a fuel cell to produce electricity. Perpetual motion remains an elusive goal.

At best, producing hydrogen from water is an electrically intense operation so you are just making an electrical car by proxy that actually ulltimately is powered by whatever fuel powers the generating station and the most efficient is atomic but there are plenty of coal fired ones too. Gee, just what we need atomic or coal powered cars. That sure would be an improvement over gasoline, at least if the generating plant weren't in your backyard or upwind of you.

I'm reminded of the folks with electric cars who think they are saving the world because they are using "clean" energy with no thought given to where the electricity comes from or the environmental impact of its generation.

To be practical you either need lots of cheap electricity to use in electrolysis to produce the hydrogen (where is cold fusion when you need it?), or another source like hydrocarbons to take apart for the hydrogen. Hydrocarbon fuels are not a readily recycleable fuel. A plus for taking hydrocarbons apart is that you can burn just the hydrogen and throw away the carbon without burning it to get carbon dioxide or monoxide. The downside is that your mileage calculated on the galons of original hydrocarbons isn't very good and the cost is pretty steep BUT you have lowered emissions...maybe. You can at least shift polution from one location to another. Yo can make a mess in one area to generate fuel to be burned cleanly in another. Maybe we could put some of the processing plants in Bopal, India as I understand their last big industrial enterprise didn't work out too well.

Biodiesel is definitely an alternative and if you drive much you'd get plenty of time consuming practice at making it. Commercial biodiesel will never be replaced by home brew. Few people will repetitively invest the time handling noxious and dangerous materials (lye etc.) required to keep making batches of fuel. Feed stocks are getting harder to come by for free or cheap and the more folks competing for them the harder it gets.

There are dedicated folks who will do it, at least for a while, but it will never have mass appeal. //SOAPBOX MODE OFF//

Ric, don't take this as a personal attack. Ask anyone, I just "GO OFF" every so often for no discernable reason and the above is one of the milder examples.

There are vehicles that get great economy and have low polution and actually do make a realistic contribution to great fuel economy and clean environment. Take for example the Toyota Prius which is head and shoulders ahead of the competition if both mileage and polution are considered. Unfortunately they are in high demand and short supply. I have had a deposit down to get one for over two months and expect to wait till March or longer to get mine. The Prius isn't magic but it has the best cross product of economy and polution of any practical commercially available car.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[ric]

Pat, you should learn say what you really think when a subject you feel strongly about comes up on this board... I think you'd really feel some satisfaction by expressing your true feelings.

Non-mainstream alternatives especially to energy use, really require commitiment on the part of the user. I use pump gas and drive old trucks that are paid for and run great.

I know two people who make and use biodiesel and they seem happy with their investment and the results. Not for me. I know one person who successfully created a water powered VW dune buggy. It was one of those people in that apartment meeting I mentioned earlier. Turned out very nice. In fact, it was on TV a couple times about 15 years ago. As I recall it had three tanks one for water and one each to store hydrogen and oxygen. The power source to start the engine and "crack" the water was a battery and step up transformer the size of your head. The water source could be tap water or distilled water. Don't know what happened to the owner or the car after it was sold.

Go get your Prius deposit back as soon as you can. The cost verses benefit of owning one of these is on the cost side and will only get worse when the batteries die. Toyota will not quote how much replacement batteries will cost because they cost so much. The Prius and Insight are really very expensive cars to build and the mfgr's are giving them away in order to sell them. You are better off buying a gas powered econo box.

Later